Organic matter

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Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come from the feces and remains of organisms such as plants and animals. [1] Organic molecules can also be made by chemical reactions that do not involve life. [2] Basic structures are created from cellulose, tannin, cutin, and lignin, along with other various proteins, lipids, and carbohydrates. Organic matter is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet. [3]

Contents

Formation

Living organisms are composed of organic compounds. In life, they secrete or excrete organic material into their environment, shed body parts such as leaves and roots and after organisms die, their bodies are broken down by bacterial and fungal action. Larger molecules of organic matter can be formed from the polymerization of different parts of already broken down matter.[ citation needed ] The composition of natural organic matter depends on its origin, transformation mode, age, and existing environment, thus its bio-physicochemical functions vary with different environments. [4]

Natural ecosystem functions

Organic matter is common throughout the ecosystem and is cycled through decomposition processes by soil microbial communities that are crucial for nutrient availability. [5] After degrading and reacting, it can move into soil and mainstream water via waterflow. Organic matter provides nutrition to living organisms. Organic matter acts as a buffer in aqueous solutions to maintain a neutral pH in the environment. The buffer acting component has been proposed to be relevant for neutralizing acid rain. [6]

Source cycle

Some organic matter not already in the soil comes from groundwater. When the groundwater saturates the soil or sediment around it, organic matter can freely move between the phases. Groundwater has its own sources of natural organic matter including:

Organisms decompose into organic matter, which is then transported and recycled. Not all biomass migrates, some is rather stationary, turning only over the course of millions of years. [8]

Soil organic matter

The organic matter in soil derives from plants, animals and microorganisms. In a forest, for example, leaf litter and woody materials fall to the forest floor. This is sometimes referred to as organic material. [9] When it decays to the point in which it is no longer recognizable, it is called soil organic matter. When the organic matter has broken down into a stable substance that resists further decomposition it is called humus. Thus soil organic matter comprises all of the organic matter in the soil exclusive of the material that has not decayed. [10]

An important property of soil organic matter is that it improves the capacity of a soil to hold water and nutrients, and allows their slow release, thereby improving the conditions for plant growth. Another advantage of humus is that it helps the soil to stick together which allows nematodes, or microscopic bacteria, to easily decay the nutrients in the soil. [11]

There are several ways to quickly increase the amount of humus. Combining compost, plant or animal materials/waste, or green manure with soil will increase the amount of humus in the soil.

  1. Compost: decomposed organic material.
  2. Plant and animal material and waste: dead plants or plant waste such as leaves or bush and tree trimmings, or animal manure.
  3. Green manure: plants or plant material that is grown for the sole purpose of being incorporated with soil.

These three materials supply nematodes and bacteria with nutrients for them to thrive and produce more humus, which will give plants enough nutrients to survive and grow. [11]

Soil organic matter is crucial to all ecology and to all agriculture, but it is especially emphasized in organic farming, where it is relied upon especially heavily.

Priming effect

The priming effect is characterized by intense changes in the natural process of soil organic matter (SOM) turnover, resulting from relatively moderate intervention with the soil. [12] The phenomenon is generally caused by either pulsed or continuous changes to inputs of fresh organic matter (FOM). [13] Priming effects usually result in an acceleration of mineralization due to a trigger such as the FOM inputs. The cause of this increase in decomposition has often been attributed to an increase in microbial activity resulting from higher energy and nutrient availability released from the FOM. After the input of FOM, specialized microorganisms are believed to grow quickly and only decompose this newly added organic matter. [14] The turnover rate of SOM in these areas is at least one order of magnitude higher than the bulk soil. [13]

Other soil treatments, besides organic matter inputs, which lead to this short-term change in turnover rates, include "input of mineral fertilizer, exudation of organic substances by roots, mere mechanical treatment of soil or its drying and rewetting." [12]

Priming effects can be either positive or negative depending on the reaction of the soil with the added substance. A positive priming effect results in the acceleration of mineralization while a negative priming effect results in immobilization, leading to N unavailability. Although most changes have been documented in C and N pools, the priming effect can also be found in phosphorus and sulfur, as well as other nutrients. [12]

Löhnis was the first to discover the priming effect phenomenon in 1926 through his studies of green manure decomposition and its effects on legume plants in soil. He noticed that when adding fresh organic residues to the soil, it resulted in intensified mineralization by the humus N. It was not until 1953, though, that the term priming effect was given by Bingeman in his paper titled, The effect of the addition of organic material on the decomposition of an organic soil. Several other terms had been used before priming effect was coined, including priming action, added nitrogen interaction (ANI), extra N and additional N. [12] Despite these early contributions, the concept of the priming effect was widely disregarded until about the 1980s-1990s. [13]

The priming effect has been found in many different studies and is regarded as a common occurrence, appearing in most plant soil systems. [15] However, the mechanisms which lead to the priming effect are more complex than originally thought, and still remain generally misunderstood. [14]

Although there is a lot of uncertainty surrounding the reason for the priming effect, a few undisputed facts have emerged from the collection of recent research:

  1. The priming effect can arise either instantaneously or very shortly (potentially days or weeks) [13] after the addition of a substance is made to the soil.
  2. The priming effect is larger in soils that are rich in C and N as compared to those poor in these nutrients.
  3. Real priming effects have not been observed in sterile environments.
  4. The size of the priming effect increases as the amount of added treatment to the soil increases. [12]

Recent findings suggest that the same priming effect mechanisms acting in soil systems may also be present in aquatic environments, which suggests a need for broader considerations of this phenomenon in the future. [13] [16]

Decomposition

One suitable definition of organic matter is biological material in the process of decaying or decomposing, such as humus. A closer look at the biological material in the process of decaying reveals so-called organic compounds (biological molecules) in the process of breaking up (disintegrating).

The main processes by which soil molecules disintegrate are by bacterial or fungal enzymatic catalysis. If bacteria or fungi were not present on Earth, the process of decomposition would have proceeded much slower.

Various factors impact the decomposition of organic matter including its chemical properties and other environmental parameters. Metabolic capabilities of the microbial communities play a crucial role on decomposition since they are highly connected with the energy availability and processing. [17] In terrestrial ecosystems the energy status of soil organic matter has been shown to affect microbial substrate preferences. [18] Some organic matter pools may be energetically favorable for the microbial communities resulting in their fast oxidation and decomposition, in comparison with other pools where microbial degraders get less return from the energy they invest. By extension, soil microorganisms preferentially mineralize high-energy organic matter, avoiding decomposing less energetically dense organic matter. [19]

Organic chemistry

Measurements of organic matter generally measure only organic compounds or carbon, and so are only an approximation of the level of once living or decomposed matter. Some definitions of organic matter likewise only consider "organic matter" to refer to only the carbon content or organic compounds and do not consider the origins or decomposition of the matter. In this sense, not all organic compounds are created by living organisms, and living organisms do not only leave behind organic material. A clam's shell, for example, while biotic, does not contain much organic carbon, so it may not be considered organic matter in this sense. Conversely, urea is one of many organic compounds that can be synthesized without any biological activity.

Organic matter is heterogeneous and very complex. Generally, organic matter, in terms of weight, is: [6]

The molecular weights of these compounds can vary drastically, depending on if they repolymerize or not, from 200 to 20,000 amu. Up to one-third of the carbon present is in aromatic compounds in which the carbon atoms form usually six-membered rings. These rings are very stable due to resonance stabilization, so they are challenging to break down. The aromatic rings are also susceptible to electrophilic and nucleophilic attacks from other electron-donating or electron-accepting material, which explains the possible polymerization to create larger molecules of organic matter.

Some reactions occur with organic matter and other materials in the soil to create compounds never seen before. Unfortunately, it is challenging to characterize these because so little is known about natural organic matter in the first place. Research is currently being done to determine more about these new compounds and how many are being formed. [20]

Aquatic

Aquatic organic matter can be further divided into two components: (1) dissolved organic matter (DOM), measured as colored dissolved organic matter (CDOM) or dissolved organic carbon (DOC), and (2) particulate organic matter (POM). They are typically differentiated by that which can pass through a 0.45 micrometre filter (DOM), and that which cannot (POM).

Detection

Organic matter is important in water and wastewater treatment and recycling, natural aquatic ecosystems, aquaculture, and environmental rehabilitation. It is, therefore, important to have reliable methods of detection and characterisation, for both short- and long-term monitoring. Various analytical detection methods for organic matter have existed for up to decades to describe and characterise organic matter. These include, but are not limited to: total and dissolved organic carbon, mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, UV-Visible spectroscopy, and fluorescence spectroscopy. Each of these methods has its advantages and limitations.

Water purification

The same capability of natural organic matter that helps with water retention in the soil creates problems for current water purification methods. In water, organic matter can still bind to metal ions and minerals. The purification process does not necessarily stop these bound molecules but does not cause harm to any humans, animals, or plants. However, because of the high reactivity of organic matter, by-products that do not contain nutrients can be made. These by-products can induce biofouling, which essentially clogs water filtration systems in water purification facilities, as the by-products are larger than membrane pore sizes. This clogging problem can be treated by chlorine disinfection (chlorination), which can break down residual material that clogs systems. However, chlorination can form disinfection by-products. [20]

Water with organic matter can be disinfected with ozone-initiated radical reactions. The ozone (three oxygens) has powerful oxidation characteristics. It can form hydroxyl radicals (OH) when it decomposes, which will react with the organic matter to shut down the problem of biofouling. [21]

Vitalism

The equation of "organic" with living organisms comes from the now-abandoned idea of vitalism, which attributed a special force to life that alone could create organic substances. This idea was first questioned after Friedrich Wöhler artificially synthesized urea in 1828.

See also

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Related Research Articles

<span class="mw-page-title-main">Compost</span> Mixture used to improve soil fertility

Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by decomposing plant and food waste, recycling organic materials, and manure. The resulting mixture is rich in plant nutrients and beneficial organisms, such as bacteria, protozoa, nematodes, and fungi. Compost improves soil fertility in gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers. The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial microbes that help to suppress pathogens in the soil and reduce soil-borne diseases.

<span class="mw-page-title-main">Ecosystem</span> Community of living organisms together with the nonliving components of their environment

An ecosystem is a system that environments and their organisms form through their interaction. The biotic and abiotic components are linked together through nutrient cycles and energy flows.

<span class="mw-page-title-main">Humus</span> Organic matter in soils resulting from decay of plant and animal materials

In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground".

<span class="mw-page-title-main">Soil</span> Mixture of organic matter, minerals, gases, liquids, and organisms that together support life

Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.

<span class="mw-page-title-main">Decomposition</span> Process in which organic substances are broken down into simpler organic matter

Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is essential for recycling the finite matter that occupies physical space in the biosphere. Bodies of living organisms begin to decompose shortly after death. Animals, such as earthworms, also help decompose the organic materials. Organisms that do this are known as decomposers or detritivores. Although no two organisms decompose in the same way, they all undergo the same sequential stages of decomposition. The science which studies decomposition is generally referred to as taphonomy from the Greek word taphos, meaning tomb. Decomposition can also be a gradual process for organisms that have extended periods of dormancy.

<span class="mw-page-title-main">Green manure</span> Organic material left on an agricultural field to be used as a mulch or soil amendment

In agriculture, a green manure is a crop specifically cultivated to be incorporated into the soil while still green. Typically, the green manure's biomass is incorporated with a plow or disk, as is often done with (brown) manure. The primary goal is to add organic matter to the soil for its benefits. Green manuring is often used with legume crops to add nitrogen to the soil for following crops, especially in organic farming, but is also used in conventional farming.

Decomposers are organisms that break down dead organisms and release the nutrients from the dead matter into the environment around them. Decomposition relies on chemical processes similar to digestion in animals; in fact, many sources use the words digestion and decomposition interchangeably. In both processes, complex molecules are chemically broken down by enzymes into simpler, smaller ones. The term "digestion," however, is commonly used to refer to food breakdown that occurs within animal bodies, and results in the absorption of nutrients from the gut into the animal's bloodstream. This is contrasted with external digestion, meaning that, rather than swallowing food and then digesting it using enzymes located within a GI tract, an organism instead releases enzymes directly onto the food source. After allowing the enzymes time to digest the material, the decomposer then absorbs the nutrients from the environment into its cells. Decomposition is often erroneously conflated with this process of external digestion, probably because of the strong association between fungi, which are external digesters, and decomposition.

<span class="mw-page-title-main">Humic substance</span> Major component of natural organic matter

Humic substances (HS) are colored relatively recalcitrant organic compounds naturally formed during long-term decomposition and transformation of biomass residues. The color of humic substances varies from bright yellow to light or dark brown leading to black. The term comes from humus, which in turn comes from the Latin word humus, meaning "soil, earth". Humic substances represent the major part of organic matter in soil, peat, coal, and sediments, and are important components of dissolved natural organic matter (NOM) in lakes, rivers, and sea water. Humic substances account for 50 – 90% of cation exchange capacity in soils.

<span class="mw-page-title-main">Organic fertilizer</span> Fertilizer developed from natural processes

Organic fertilizers are fertilizers that are naturally produced. Fertilizers are materials that can be added to soil or plants, in order to provide nutrients and sustain growth. Typical organic fertilizers include all animal waste including meat processing waste, manure, slurry, and guano; plus plant based fertilizers such as compost; and biosolids. Inorganic "organic fertilizers" include minerals and ash. Organic refers to the Principles of Organic Agriculture, which determines whether a fertilizer can be used for commercial organic agriculture, not whether the fertilizer consists of organic compounds.

<span class="mw-page-title-main">Detritus</span> Dead particulate organic material

In biology, detritus is organic matter made up of the decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decompose (remineralise) it. Such microorganisms may be decomposers, detritivores, or coprophages.

<span class="mw-page-title-main">Dissolved organic carbon</span> Organic carbon classification

Dissolved organic carbon (DOC) is the fraction of organic carbon operationally defined as that which can pass through a filter with a pore size typically between 0.22 and 0.7 micrometers. The fraction remaining on the filter is called particulate organic carbon (POC).

<span class="mw-page-title-main">Soil biology</span> Study of living things in soil

Soil biology is the study of microbial and faunal activity and ecology in soil. Soil life, soil biota, soil fauna, or edaphon is a collective term that encompasses all organisms that spend a significant portion of their life cycle within a soil profile, or at the soil-litter interface. These organisms include earthworms, nematodes, protozoa, fungi, bacteria, different arthropods, as well as some reptiles, and species of burrowing mammals like gophers, moles and prairie dogs. Soil biology plays a vital role in determining many soil characteristics. The decomposition of organic matter by soil organisms has an immense influence on soil fertility, plant growth, soil structure, and carbon storage. As a relatively new science, much remains unknown about soil biology and its effect on soil ecosystems.

Soil chemistry is the study of the chemical characteristics of soil. Soil chemistry is affected by mineral composition, organic matter and environmental factors. In the early 1870s a consulting chemist to the Royal Agricultural Society in England, named J. Thomas Way, performed many experiments on how soils exchange ions, and is considered the father of soil chemistry. Other scientists who contributed to this branch of ecology include Edmund Ruffin, and Linus Pauling.

<span class="mw-page-title-main">Immobilization (soil science)</span>

Immobilization in soil science is the conversion of inorganic compounds to organic compounds by microorganisms or plants by which the compounds become inaccessible to plants. Immobilization is the opposite of mineralization. In immobilization, inorganic nutrients are taken up by soil microbes and become unavailable for plant uptake. Immobilization is therefore a biological process controlled by bacteria that consume inorganic nitrogen and form amino acids and biological macromolecules. Immobilization and mineralization are continuous processes that occur concurrently whereby nitrogen of the decomposing system is steadily transformed from an inorganic to an organic state by immobilization and from an organic to an inorganic state by decay and mineralization.

In soil science, mineralization is the decomposition of the chemical compounds in organic matter, by which the nutrients in those compounds are released in soluble inorganic forms that may be available to plants. Mineralization is the opposite of immobilization.

<span class="mw-page-title-main">Microbial loop</span> Trophic pathway in marine microbial ecosystems

The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. In soil systems, the microbial loop refers to soil carbon. The term microbial loop was coined by Farooq Azam, Tom Fenchel et al. in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.

Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous benefits to soil's physical and chemical properties and its capacity to provide regulatory ecosystem services. SOM is especially critical for soil functions and quality.

<span class="mw-page-title-main">Mycorrhizal fungi and soil carbon storage</span> Terrestrial ecosystem

Soil carbon storage is an important function of terrestrial ecosystems. Soil contains more carbon than plants and the atmosphere combined. Understanding what maintains the soil carbon pool is important to understand the current distribution of carbon on Earth, and how it will respond to environmental change. While much research has been done on how plants, free-living microbial decomposers, and soil minerals affect this pool of carbon, it is recently coming to light that mycorrhizal fungi—symbiotic fungi that associate with roots of almost all living plants—may play an important role in maintaining this pool as well. Measurements of plant carbon allocation to mycorrhizal fungi have been estimated to be 5 to 20% of total plant carbon uptake, and in some ecosystems the biomass of mycorrhizal fungi can be comparable to the biomass of fine roots. Recent research has shown that mycorrhizal fungi hold 50 to 70 percent of the total carbon stored in leaf litter and soil on forested islands in Sweden. Turnover of mycorrhizal biomass into the soil carbon pool is thought to be rapid and has been shown in some ecosystems to be the dominant pathway by which living carbon enters the soil carbon pool.

Priming or a "priming effect" is said to occur when something that is added to soil or compost affects the rate of decomposition occurring on the soil organic matter (SOM), either positively or negatively. Organic matter is made up mostly of carbon and nitrogen, so adding a substrate containing certain ratios of these nutrients to soil may affect the microbes that are mineralizing SOM. Fertilizers, plant litter, detritus, and carbohydrate exudates from living roots, can potentially positively or negatively prime SOM decomposition.

<span class="mw-page-title-main">Particulate organic matter</span>

Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 millimeters (53 μm) to 2 millimeters.

References

  1. ↑ "Natural Organic Matter". GreenFacts. Retrieved 28 July 2019.
  2. ↑ "NASA Goddard Instrument Makes First Detection of Organic Matter on Mars". NASA. 16 December 2014. Retrieved 28 July 2019.
  3. ↑ Sejian, Veerasamy; Gaughan, John; Baumgard, Lance; Prasad, Cadaba (31 March 2015). Climate Change Impact on Livestock: Adaptation and Mitigation. Springer. ISBN   978-81-322-2265-1.
  4. ↑ Nicola Senesi, Baoshan Xing, and P.M. Huang, Biophysico-Chemical Processes Involving Natural Nonlifiidulfitving Organic Matter in Environmental Systems, New York: IUPAC, 2006.
  5. ↑ Ochoa-Hueso, R; Delgado-Baquerizo, M; King, PTA; Benham, M; Arca, V; Power, SA (2019). "Ecosystem type and resource quality are more important than global change drivers in regulating early stages of litter decomposition". Soil Biology and Biochemistry. 129: 144–152. Bibcode:2019SBiBi.129..144O. doi:10.1016/j.soilbio.2018.11.009. hdl: 10261/336676 . S2CID   92606851.
  6. 1 2 Steve Cabaniss, Greg Madey, Patricia Maurice, Yingping Zhou, Laura Leff, Olacheesy head Bob Wetzel, Jerry Leenheer, and Bob Wershaw, comps, Stochastic Synthesis of Natural Organic Matter, UNM, ND, KSU, UNC, USGS, 22 Apr 2007.
  7. ↑ George Aiken (2002). "Organic Matter in Ground Water". United States Geological Survey. Retrieved 28 July 2019.
  8. ↑ Tori M. Hoehler & Bo Barker Jørgensen "Microbial life under extreme energy limitation" Nature Reviews Microbiology 2013, vol 11, p 83 doi : 10.1038/nrmicro2939
  9. ↑ "Organic Materials". U.S. Environmental Protection Agency. Archived from the original on 25 September 2006. Retrieved 19 November 2006.
  10. ↑ "Soil Health Terms". Archived from the original on 8 November 2006.
  11. 1 2 Crow, W. T. “Organic Matter, Green Manures and Cover Crops For Nematode Management.” [ permanent dead link ] University of Florida. The Institute of Food and Agricultural Sciences Feb. 2009 Web 10 October 2009
  12. 1 2 3 4 5 Kuzyakov, Y.; Friedel, J.K.; Stahr, K. (October 2000). "Review of mechanisms and quantification of priming effects". Soil Biology & Biochemistry. 32 (11–12): 1485–1498. Bibcode:2000SBiBi..32.1485K. doi:10.1016/S0038-0717(00)00084-5.
  13. 1 2 3 4 5 Kuzyakov, Y. (2010). "Priming effects: Interactions between living and dead organic matter". Soil Biology & Biochemistry. 42 (9): 1363–1371. Bibcode:2010SBiBi..42.1363K. doi:10.1016/J.Soilbio.2010.04.003.
  14. 1 2 Fontaine, Sebastien; Mariotti, Abbadie (2003). "The priming effect of organic matter: a question of microbial competition?". Soil Biology & Biochemistry. 35 (6): 837–843. Bibcode:2003SBiBi..35..837F. doi:10.1016/s0038-0717(03)00123-8.
  15. ↑ Nottingham, A.T.; Griffiths, Chamberlain; Stott, Tanner (2009). "Soil priming by sugar and leaf-litter substrates: A link to microbial groups". Applied Soil Ecology. 42 (3): 183–190. Bibcode:2009AppSE..42..183N. doi:10.1016/J.Apsoil.2009.03.003.
  16. ↑ Guenet, B.; Danger; Abbadie; Lacroix (October 2010). "Priming effect:bridging the gap between terrestrial and aquatic ecology". Ecology. 91 (10): 2850–2861. Bibcode:2010Ecol...91.2850G. doi:10.1890/09-1968.1. PMID   21058546.
  17. ↑ Wang, Chaoqun; Kuzyakov, Yakov (November 2023). "Energy use efficiency of soil microorganisms: Driven by carbon recycling and reduction". Global Change Biology. 29 (22): 6170–6187. doi: 10.1111/gcb.16925 . ISSN   1354-1013. PMID   37646316.
  18. ↑ Williams, Elizabeth K.; Plante, Alain F. (26 September 2018). "A Bioenergetic Framework for Assessing Soil Organic Matter Persistence". Frontiers in Earth Science. 6: 143. Bibcode:2018FrEaS...6..143W. doi: 10.3389/feart.2018.00143 . ISSN   2296-6463.
  19. ↑ Barré, Pierre; Plante, Alain F.; Cécillon, Lauric; Lutfalla, Suzanne; Baudin, François; Bernard, Sylvain; Christensen, Bent T.; Eglin, Thomas; Fernandez, Jose M.; Houot, Sabine; Kätterer, Thomas; Le Guillou, Corentin; Macdonald, Andy; van Oort, Folkert; Chenu, Claire (October 2016). "The energetic and chemical signatures of persistent soil organic matter". Biogeochemistry. 130 (1–2): 1–12. Bibcode:2016Biogc.130....1B. doi:10.1007/s10533-016-0246-0. ISSN   0168-2563.
  20. 1 2 "Topic Snapshot: Natural Organic Material", American Water Works Association Research Foundation, 2007, 22 April 2007 Archived 28 September 2007 at the Wayback Machine
  21. ↑ Cho, Min, Hyenmi Chung, and Jeyong Yoon, "Disinfection of Water Containing Natural Organic Matter by Using Ozone-Initiated Radical Reactions," Abstract, Applied and Environmental Microbiology Vol. 69 No.4 (2003): 2284-2291.

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